The present invention relates generally to radiographic detectors and, more particularly, to an x-ray detector that may be quickly detached from an x-ray scanner when not in use.
X-ray imaging is a non-invasive technique to capture images of medical patients for clinical diagnosis as well as inspect the contents of sealed containers, such as luggage, packages, and other parcels. To capture these images, an x-ray source irradiates a scan subject with a fan beam of x-rays. The x-rays are then attenuated as they pass through the scan subject. The degree of attenuation varies across the scan subject as a result of variances in the internal composition of the subject. The attenuated energy impinges upon an x-ray detector designed to convert the attenuating energy to a form usable in image reconstruction. A control system reads out electrical charge stored in the x-ray detector and generates a corresponding image. For a conventional, screen film detector, the image is developed on a film and displayed using a backlight.
Increasingly, flat panel, digital x-ray detectors are being used to acquire data for image reconstruction. Flat panel detectors are generally constructed as having a scintillator, which is used to convert x-rays to visible light that can be detected by a photosensitive layer. The photosensitive layer includes an array of photosensitive or detection elements that each store electrical charge in proportion to the light that is individually detected. Generally, each detection element has a light sensitive region and a region comprised of electronics to control the storage and output of electrical charge. The light sensitive region is typically composed of a photoconductor, and electrons are released in the photoconductor when exposed to visible light. During this exposure, charge is collected in each detector element and is stored in a capacitor situated in the electronics region. After exposure, the charge in each detector element is read out using logic controlled electronics.
Each detector element is conventionally controlled using a transistor-based switch. In this regard, the source of the transistor is connected to the capacitor, the drain of the transistor is connected to a readout line, and the gate of the transistor is connected to a scan control interface disposed on the electronics in the detector. When negative voltage is applied to the gate, the switch is driven to an OFF state, i.e. no conduction between the source and drain. On the other hand, when a positive voltage is applied to the gate, the switch is turned ON resulting in connection of the source to the drain. Each detector element of the detector array is constructed with a respective transistor and is controlled in a manner consistent with that described below.
Specifically, during exposure to x-rays, negative voltage is applied to all gate lines resulting in all the transistor switches being driven to or placed in an OFF state. As a result, any charge accumulated during exposure is stored in each detector element capacitor. During read out, positive voltage is sequentially applied to each gate line, one gate at a time. In this regard, only one detector element is read out at a time. A multiplexer may also be used to support read out of the detector elements in a raster fashion. An advantage of sequentially reading out each detector element individually is that the charge from one detector element does not pass through any other detector elements. The output of each detector element is then input to a digitizer that digitizes the acquired signals for subsequent image reconstruction on a per pixel basis. Each pixel of the reconstructed image corresponds to a single detector element of the detector array.
Conventional x-ray detectors are usually fixedly attached to an x-ray scanner through cables and/or wires bundled together through a tether to facilitate the supply of power to the detector and to facilitate communication therebetween. The tether cables and/or wires are typically fixed to the detector and x-ray scanner such that separation of the detector from the x-ray scanner is possible only by a qualified technician. For example, the cables and/or wires are often located behind a non-user serviceable panel, thus requiring a service call from a qualified technician to access the tether connections.
This fixed connection of an x-ray detector to an x-ray scanner across a tether has a number of drawbacks. For example, a tether can be crushed or bent as it lays exposed on the floor. In another example, the x-ray detector may become damaged if it falls onto the floor through operator mishandling or through being pulled to the floor by the fixed tether when the tether is snagged. Damage caused either to the tether or to the x-ray detector when the tether is fixed to the x-ray detector and/or x-ray scanner requires that a service call be made to request that a qualified technician replace or repair the damaged components. An end-user is typically not trained for servicing internal components of the x-ray scanner or x-ray detector and damage to sensitive components other than the tether may occur if the end-user attempts to remove a fixed tether. As a result, the x-ray detector must be removed from use until serviced, which decreases subject throughput.
Additionally, a tethered connection between the x-ray detector and x-ray scanner can increase the difficulty of positioning the x-ray detector for imaging. This is particularly problematic when the x-ray detector must be placed at an awkward angle or an x-ray is to be taken in an operation room or other sterile facility. That is, an x-ray may be required of a patient during a surgical procedure and, as is well known, it is desirable to maintain a sterile environment. The tether may not be sterile and come in contact with an otherwise sterile environment as a radiologist or other user is placing the detector for data acquisition.
Therefore, it would be desirable to design an x-ray scanner that can be easily, quickly, and repeatedly detached from an x-ray scanner.